[FFmpeg-cvslog] mp3enc: mux a XING header
Peter Belkner
git at videolan.org
Sat May 7 04:07:34 CEST 2011
ffmpeg | branch: master | Peter Belkner <pbelkner at snafu.de> | Sat May 7 02:23:28 2011 +0200| [d62bf5d4e73250295c0a652e151498c5b19cbd63] | committer: Michael Niedermayer
mp3enc: mux a XING header
The patch below provides exactly that to the MP3 muxer. A XING header
containing
* the numer of frames,
* the size, and
* a TOC
is generated.
It's based on an idea by Anton Khirnov (restricted to the number of
frames) found at
http://patches.ffmpeg.org/patch/1891/
The TOC is generated as found in lame's "VbrTag.c".
According to my tests the following reproduces the number of frames, the
size and the TOC in "c.mp3" from "b.mp3" (except a shift due to shorter
XING header generated by FFmpeg):
lame -V2 a.wav b.mp3
ffmpeg -i b.mp3 -acodec copy -y c.mp3
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=d62bf5d4e73250295c0a652e151498c5b19cbd63
---
libavformat/mp3enc.c | 229 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 226 insertions(+), 3 deletions(-)
diff --git a/libavformat/mp3enc.c b/libavformat/mp3enc.c
index 9b02050..8150b78 100644
--- a/libavformat/mp3enc.c
+++ b/libavformat/mp3enc.c
@@ -27,6 +27,9 @@
#include "libavutil/avstring.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/opt.h"
+#include "libavcodec/mpegaudiodata.h"
+#include "libavcodec/mpegaudiodecheader.h"
+#include "libavformat/avio_internal.h"
static int id3v1_set_string(AVFormatContext *s, const char *key,
uint8_t *buf, int buf_size)
@@ -127,7 +130,7 @@ static int id3v2_put_ttag(AVFormatContext *s, const char *str1, const char *str2
return len + ID3v2_HEADER_SIZE;
}
-static int mp3_write_trailer(struct AVFormatContext *s)
+static int mp2_write_trailer(struct AVFormatContext *s)
{
uint8_t buf[ID3v1_TAG_SIZE];
@@ -150,14 +153,29 @@ AVOutputFormat ff_mp2_muxer = {
CODEC_ID_NONE,
NULL,
ff_raw_write_packet,
- mp3_write_trailer,
+ mp2_write_trailer,
};
#endif
#if CONFIG_MP3_MUXER
+#define VBR_NUM_BAGS 400
+#define VBR_TOC_SIZE 100
typedef struct MP3Context {
const AVClass *class;
int id3v2_version;
+ struct xing_header {
+ int64_t offset;
+ int32_t frames;
+ int32_t size;
+ /* following lame's "VbrTag.c". */
+ struct xing_toc {
+ uint32_t want;
+ uint32_t seen;
+ uint32_t pos;
+ uint64_t sum;
+ uint64_t bag[VBR_NUM_BAGS];
+ } toc;
+ } xing_header;
} MP3Context;
static const AVOption options[] = {
@@ -188,6 +206,156 @@ static int id3v2_check_write_tag(AVFormatContext *s, AVMetadataTag *t, const cha
return -1;
}
+static const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
+static const uint32_t XING = MKBETAG('X', 'i', 'n', 'g');
+#ifdef FILTER_VBR_HEADERS
+static const uint32_t INFO = MKBETAG('I', 'n', 'f', 'o');
+static const uint32_t VBRI = MKBETAG('V', 'B', 'R', 'I');
+#endif
+
+/*
+ * Write an empty XING header and initialize respective data.
+ */
+static int mp3_write_xing(AVFormatContext *s)
+{
+ AVCodecContext *codec = s->streams[0]->codec;
+ MP3Context *mp3 = s->priv_data;
+ int bitrate_idx = 3;
+ int64_t xing_offset;
+ int32_t mask, header;
+ MPADecodeHeader c;
+ int srate_idx, i, channels;
+ int needed;
+
+ for (i = 0; i < FF_ARRAY_ELEMS(ff_mpa_freq_tab); i++)
+ if (ff_mpa_freq_tab[i] == codec->sample_rate) {
+ srate_idx = i;
+ break;
+ }
+ if (i == FF_ARRAY_ELEMS(ff_mpa_freq_tab)) {
+ av_log(s, AV_LOG_ERROR, "Unsupported sample rate.\n");
+ return -1;
+ }
+
+ switch (codec->channels) {
+ case 1: channels = MPA_MONO; break;
+ case 2: channels = MPA_STEREO; break;
+ default: av_log(s, AV_LOG_ERROR, "Unsupported number of channels.\n"); return -1;
+ }
+
+ /* dummy MPEG audio header */
+ header = 0xff << 24; // sync
+ header |= (0x7 << 5 | 0x3 << 3 | 0x1 << 1 | 0x1) << 16; // sync/mpeg-1/layer 3/no crc*/
+ header |= (srate_idx << 2) << 8;
+ header |= channels << 6;
+
+ for (;;) {
+ if (15 == bitrate_idx)
+ return -1;
+
+ mask = (bitrate_idx << 4) << 8;
+ header |= mask;
+ ff_mpegaudio_decode_header(&c, header);
+ xing_offset=xing_offtbl[c.lsf == 1][c.nb_channels == 1];
+ needed = 4 // header
+ + xing_offset
+ + 4 // xing tag
+ + 4 // frames/size/toc flags
+ + 4 // frames
+ + 4 // size
+ + VBR_TOC_SIZE; // toc
+
+ if (needed <= c.frame_size)
+ break;
+
+ header &= ~mask;
+ ++bitrate_idx;
+ }
+
+ avio_wb32(s->pb, header);
+ ffio_fill(s->pb, 0, xing_offset);
+ avio_wb32(s->pb, XING);
+ avio_wb32(s->pb, 0x01 | 0x02 | 0x04); // frames/size/toc
+
+ mp3->xing_header.offset = avio_tell(s->pb);
+ mp3->xing_header.size = c.frame_size;
+ mp3->xing_header.toc.want=1;
+ mp3->xing_header.toc.seen=0;
+ mp3->xing_header.toc.pos=0;
+ mp3->xing_header.toc.sum=0;
+
+ avio_wb32(s->pb, 0); // frames
+ avio_wb32(s->pb, 0); // size
+
+ // toc
+ for (i = 0; i < VBR_TOC_SIZE; ++i)
+ avio_w8(s->pb, (uint8_t)(255 * i / VBR_TOC_SIZE));
+
+ ffio_fill(s->pb, 0, c.frame_size - needed);
+ avio_flush(s->pb);
+
+ return 0;
+}
+
+/*
+ * Add a frame to XING data.
+ * Following lame's "VbrTag.c".
+ */
+static void mp3_xing_add_frame(AVFormatContext *s, AVPacket *pkt, MPADecodeHeader *c)
+{
+ MP3Context *mp3 = s->priv_data;
+ struct xing_header *xing_header = &mp3->xing_header;
+ struct xing_toc *toc = &xing_header->toc;
+ int i;
+
+ ++xing_header->frames;
+ xing_header->size += pkt->size;
+ toc->sum += c->bit_rate / 1000;
+
+ if (toc->want == ++toc->seen) {
+ toc->bag[toc->pos] = toc->sum;
+
+ if (VBR_NUM_BAGS == ++toc->pos) {
+ /* shrink table to half size by throwing away each second bag. */
+ for (i = 1; i < VBR_NUM_BAGS; i += 2)
+ toc->bag[i >> 1] = toc->bag[i];
+
+ /* double wanted amount per bag. */
+ toc->want <<= 1;
+ /* adjust current position to half of table size. */
+ toc->pos >>= 1;
+ }
+
+ toc->seen = 0;
+ }
+}
+
+static void mp3_fix_xing(AVFormatContext *s)
+{
+ MP3Context *mp3 = s->priv_data;
+ struct xing_header *xing_header = &mp3->xing_header;
+ struct xing_toc *toc = &xing_header->toc;
+ double scale = (double)toc->pos / (double)VBR_TOC_SIZE;
+ int i;
+
+ avio_flush(s->pb);
+ avio_seek(s->pb, xing_header->offset, SEEK_SET);
+ avio_wb32(s->pb, xing_header->frames);
+ avio_wb32(s->pb, xing_header->size);
+
+ avio_w8(s->pb, 0); // first toc entry has to be zero.
+
+ for (i = 1; i < VBR_TOC_SIZE; ++i) {
+ int j = (int)floor(scale * i);
+ int seek_point = (int)floor(256.0 * toc->bag[j] / toc->sum);
+
+ avio_w8(s->pb, (uint8_t)(seek_point < 256 ? seek_point : 255));
+ }
+
+ avio_flush(s->pb);
+ avio_seek(s->pb, 0, SEEK_END);
+}
+
/**
* Write an ID3v2 header at beginning of stream
*/
@@ -236,6 +404,61 @@ static int mp3_write_header(struct AVFormatContext *s)
id3v2_put_size(s, totlen);
avio_seek(s->pb, cur_pos, SEEK_SET);
+ if (s->pb->seekable)
+ mp3_write_xing(s);
+
+ return 0;
+}
+
+static int mp3_write_packet(AVFormatContext *s, AVPacket *pkt)
+{
+ if (! pkt || ! pkt->data || pkt->size < 4)
+ return ff_raw_write_packet(s, pkt);
+ else {
+ MP3Context *mp3 = s->priv_data;
+ MPADecodeHeader c;
+#ifdef FILTER_VBR_HEADERS
+ int base;
+#endif
+
+ ff_mpegaudio_decode_header(&c, AV_RB32(pkt->data));
+
+#ifdef FILTER_VBR_HEADERS
+ /* filter out XING and INFO headers. */
+ base = 4 + xing_offtbl[c.lsf == 1][c.nb_channels == 1];
+
+ if (base + 4 <= pkt->size) {
+ uint32_t v = AV_RB32(pkt->data + base);
+
+ if (XING == v || INFO == v)
+ return 0;
+ }
+
+ /* filter out VBRI headers. */
+ base = 4 + 32;
+
+ if (base + 4 <= pkt->size && VBRI == AV_RB32(pkt->data + base))
+ return 0;
+#endif
+
+ if (0 < mp3->xing_header.offset)
+ mp3_xing_add_frame(s, pkt, &c);
+
+ return ff_raw_write_packet(s, pkt);
+ }
+}
+
+static int mp3_write_trailer(AVFormatContext *s)
+{
+ MP3Context *mp3 = s->priv_data;
+ int ret=mp2_write_trailer(s);
+
+ if (ret < 0)
+ return ret;
+
+ if (0 < mp3->xing_header.offset)
+ mp3_fix_xing(s);
+
return 0;
}
@@ -248,7 +471,7 @@ AVOutputFormat ff_mp3_muxer = {
CODEC_ID_MP3,
CODEC_ID_NONE,
mp3_write_header,
- ff_raw_write_packet,
+ mp3_write_packet,
mp3_write_trailer,
AVFMT_NOTIMESTAMPS,
.priv_class = &mp3_muxer_class,
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